The present invention relates to a process for the separation of actinides from lanthanides present in the trivalent state in an aqueous nitric solution. More specifically, it relates to the selective extraction of actinides in an organic solvent containing a propane diamide.
In irradiated nuclear fuel reprocessing installations, in the first extraction stage of uranium and plutonium, aqueous solutions are obtained of fission products containing relatively large quantities of trivalent ions from the series of lanthanides and actinides. The aqueous effluents from these installations also contain the same ions.
In view of the relatively long period of actinide elements, it is of great interest to separate them from nitric aqueous solutions in order to avoid the manipulation of waste or effluents having a high alpha activity. Thus, the presence of alpha emitters with a long life such as Pu, Am, Np and Cm leads to high waste storage costs.
The presently known processes for the extraction of the actinides present in such solutions, e.g. the processes described in FR-A-2 537 326 and FR-A-2 585 692, make it possible to extract the actinides in an organic solvent, no matter what their valency state, but with these processes the trivalent lanthanides resulting from the fission products are also extracted in the organic solvent.
Thus, the ions of series 4f and 5f in the trivalent state have identical chemical properties making their separation especially difficult. However, in order to further improve the control of waste materials, it would be of interest to separate the actinides from the lanthanides.
Progress in Nuclear Energy, Series III, Process Chemistry, vol. 4, C. E. Stevenson, E. A. Mason and T. Gresky, Pergamon Press, pp 596-598 describes a process making it possible to separate actinides from lanthanides present in an aqueous solution and which uses highly concentrated complexing solutions.
Consideration has also been given to the separation of actinides from lanthanides by the selective extraction of the actinides by means of an organic extractant of the phosphonate type diluted in para-diisopropyl benzene, by adding a thiocyanate to an aqueous hydrochloric solution containing lanthanides and actinides, with a view to aiding said separation and as is described by Muscatello et al in Separation Science and Technology, 17(6), pp 859-875, 1982.
However, when it is wished to use the same separating principle with other neutral extractants such as tributyl phosphate or trioctyl phosphine oxide, a satisfactory result is not obtained, as is described by Khopkar et al in J. Inorg. Nucl. Chem., 34, pp 2617-2625, 1972.
However, it is possible to use this extraction principle with anionic extractants such as quaternary ammonium salts, as is described by Gerontopoulos et al in Radiochimica Acta, 4.2, pp 75-78, 1965.